I cherish my copy of this book of Trey's, especially since he not only signed it for me, he also added a personal note with his signature since we know each other. About the only portions of this book that are outdated are the information on 2-handed rods and lines only because there are a lot more of both available now than when he wrote the book.
I don't know how many of you know this or not; but Trey wrote other books on steelhead fly fishing before this one, although they are not as large or extensive as STEELHEAD FLY FISHING. Each of those had bibliographies and quite a bit of research went into them as well.
I haven't yet read Dec's book, although I know him as well and used to run into him a lot each spring on the Skagit or Sauk before he gave up guiding and moved to Salt Lake City. I would expect Dec's book to be a good one though because he is a very good and knowledgeable stealhead fisherman.